JPS5857182B2 - Taiji no Shinpakkeisu Hoshiki - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a fetal heart rate counting device within a mother, and more specifically, as a means of removing noise in order to ensure accurate counting, a sensitive period is set in the counting device and this period is automatically changed. It is designed to be determined variably.

Various devices of this type have been proposed in the past, and for example, Japanese Patent Publication No. 47-48757 has the following summary.

That is, conventionally, there is a method of measuring fetal heart rate using fetal electrocardiogram and fetal heart sounds, but when using fetal electrocardiogram, the signal (F) to be detected is as shown in Figure 1.
In addition to murmurs, maternal cardiac voltage (1) and respiratory agitation (2)
) and abdominal muscle muscle voltage (3) are mixed.

Among these noises, respiratory agitation (2) can be easily removed with a high-pass filter, but removal of other noises becomes a problem.

In order to remove such noise, (4) direct matrix elimination method, (
B) Coded maternal elimination method and (C) autocorrelation method have been tried, but the direct maternal elimination method and the coded maternal elimination method are for removing the maternal cardiac voltage (1). ,
There is no effect on the muscle voltage (3) of the abdominal muscles.

In addition, although the autocorrelation method can remove noise, it requires real-time operation for labor monitoring when measuring the fetal heart rate.
Requires a high-speed and fairly large-scale correlator.

Therefore, as shown in FIG. 2, the fetal heartbeat signal mixed with noise from maternal electrocardiograms, myoelectric waves, etc. is passed through a high-pass filter or band-pass filter 1, and then added to a Schmitt trigger circuit 2 for shaping. , after converting this shaped output into a pulse signal with a constant amplitude and constant width using a monostable multi-by-break 3, this is converted into a pulse signal with a constant amplitude and a constant width, and then this is passed through AND gates 4a, 4b, 4C...
4a t 4b t 4c . . .
The output signal shifted by the shift register 5 is added to the other input terminal of the AND gates 4 a , 4 b , 4 c . . . A device configured to obtain more fetal heart rate has been proposed.

Note that 6 is a shift pulse generator.

In other words, while the fetal heartbeat and the maternal cardiac voltage (1) have periodicity, the abdominal muscle voltage (3) has no periodicity and has the property of appearing irregularly. ,
Shift register 5 and AND gates 4a, 4b, 4c.
. . . to extract only periodic signals, and further to extract only fetal heartbeat signals due to the difference in period.

But in this case, AND gates 4a, 4b.

4c... When taking the autocorrelation of the fetal heart rate signal, timing deviations such as shift time and AND gate are likely to occur, making it difficult to accurately count the heart rate.
This type of device has a fatal drawback in that unless a doctor is sufficiently familiar with it, it may lead to misdiagnosis, leading to serious consequences that could affect the life of the fetus or mother.In addition, the device as a whole is large in size. At the same time, it is expensive and cannot be implemented easily.

The present invention aims to eliminate each of the above-mentioned drawbacks, and details thereof will be explained below based on illustrated embodiments.

FIG. 3 is an example of a signal waveform obtained from the mother's body using the ultrasound Doppler method or a heart sound microphone.

Such a signal waveform is not suitable for counting heart rate, so if the waveform is shaped by a known method using A, G, C, peak trigger, filter, etc., it will become a pulse waveform as shown in Figure 4. Become.

Although it is not possible to obtain a normal heart rate due to noise pulses in this state, the present invention focuses on the fact that the heart rate has periodicity, and uses the obtained previous heartbeat pulse signal to generate the next pulse. By predicting the period of , and outputting only signals that occur only during a short period before and after the predicted period, noisy pulses can be removed and the heart rate can be counted accurately.

A more detailed explanation will be given below using examples.

In FIG. 5, the area before and after the previous heartbeat cycle T, for example, ±10 to 20%, is defined as the sensitive area t1,
Other areas are insensitive areas (or prohibited areas) t2
The key point of the present invention is that the signal contained in the insensitive region t2 is removed as a noise signal, and the signal in the sensitive region t1 is obtained as a fetal heart rate signal.

FIG. 6 shows a configuration diagram of a specific embodiment of the present invention. In the same figure, 11 is an output circuit that obtains an output that is a function of the period, and a constant current source circuit, a charging/discharging circuit, etc., is used to generate a direct current proportional to the period. This is a circuit that obtains voltage.

The highest value of one of the outputs of this circuit 11 is applied to and held by a holding circuit 12 which holds it for a specific period of time.

The other output is applied to the comparison circuit 13 together with the output of the holding circuit 12, and the outputs are compared.

Since the holding circuit 12 holds the maximum value of the voltage proportional to the previous cycle T, the output of the comparator circuit 13 has a sensitive period tl (flJ, for example, ±10 to
20% value) can be obtained.

Since the output of the comparator circuit 13 is applied to the AND gate circuit 14, it is a circuit for allowing the input signal to pass only during the sensitive period and blocking the signal during the other periods to remove the noise signal.

Reference numeral 15 denotes a trigger pulse generation circuit that generates trigger pulses for controlling each of the circuits 11, 12, and 13 described above.

In this way, it is possible to remove noise signals and obtain only periodic signals, but the sensitive region t1 and the insensitive region t2 are divided into the above-mentioned circuits 11 to 12 with respect to the previous period T.
Since it is difficult to determine with only the block configuration of one system in 15, the e area is determined using the circuit configuration of the previous stage,
The circuit configurations 11 to 15 at the subsequent stage determine the region (2).

FIG. 7 is a diagram clearly showing operating waveforms in the above circuit device.

A is a signal waveform obtained by cardiac sound or ultrasound Doppler method.

1 is a pulse wave whose waveform is shaped by AGC, peak value detection, etc., which is supplied to the circuits 14 and 15, and is an input pulse wave to the present circuit device.

C shows the DC voltage waveform proportional to the input pulse interval and the state in which this maximum value is held; the solid line shows the DC voltage waveform proportional to the pulse interval at the output of the output circuit 11;
The dotted line represents the highest value of the output circuit 11 held by the holding circuit 12.

In other words, since the highest value proportional to the previous pulse interval is held, the sensitive period can be determined using this as a reference.
3, the sensitive period is determined and it becomes possible to eliminate pulses shorter than the previous pulse interval.

Two waveforms are obtained as the output of this comparison circuit 13.

By comparing the second waveform and the original mouth waveform using the AND gate circuit 14, the waveform E is obtained, and it can be seen that noise has been removed.

However, T1 to T4 obtained in E are not all treated as fetal heartbeat cycles.

Therefore, it is necessary to perform discrimination using the circuit configurations 11' to 15' to discriminate which is the heartbeat cycle.

This is the waveform of F, G, and C.

In other words, waveform E shows the DC voltage waveform proportional to the input pulse interval and the state in which the maximum value is maintained, and waveform G is obtained as the output of the comparator circuit 13'.

This waveform of G and the waveform of E above are combined into an AND gate circuit 14'.
By comparing with , the waveform of q is obtained.

The output of Q is used to distinguish T1 to T4 obtained by E as a period, and a known circuit can be used to distinguish it as a period only when there is a pulse of Q.

As a result, T1. T2. T4 is distinguished as a period, but T3 is removed.

Although this embodiment is explained in terms of proportion, the comparison in the comparison circuits 13 and 13' is performed by the holding circuits 12 and 17.
The gate voltage for a constant heart rate difference may be set by increasing or decreasing the holding voltage.

The above explanation is an example of implementation, and an integrating circuit, a digital circuit, a reverse discharge circuit, etc. can be used to obtain a voltage proportional to the pulse interval, and a holding circuit can be a circuit using an FET and a capacitor, an operational amplifier, Digital circuits can also be considered,
An operational amplifier or the like may be used as the comparison circuit.

In addition, the circuit device according to the present invention can also be constructed by using circuits such as monostable multi, OR gates, AND gates, and flip-flops.

As mentioned above, by using the circuit device of the present invention in a fetal heart rate counting device, it is possible to completely eliminate noise mixed in heart sounds, ultrasonic Doppler heart sounds, etc., and it can be carried out in an extremely simple and inexpensive manner. It has many advantages, such as fewer errors in heart rate counting and the ability to monitor delivery very easily and without error, and has great medical effects.

[Brief explanation of drawings]

FIG. 1 is an electrocardiogram showing characteristics of fetal heartbeat and noise; FIG. 2 is a systematic circuit diagram showing an example of a conventional fetal heart rate counting device;
3 is a heart waveform diagram, FIG. 4 is a waveform diagram of a pulsed signal shown in FIG. 3, FIG. 5 is an explanatory diagram showing the basic idea of this invention, and FIG. 6 is an illustration of an embodiment of this invention A systematic circuit diagram showing the main parts, and FIG. 7 is a waveform diagram for explaining the operation of the same. T...heartbeat cycle, tl...sensitive area,
t2...Insensitive area, 11, 11'...
・Output circuit, 12゜12'...Holding circuit, 13
, 13'... Comparison circuit, 14.14'...
...And gate circuit, 15,15'...Trigger pulse circuit.

Claims (1)

[Claims] 1. Waveform shaping means for shaping a signal wave synchronized with the fetal heartbeat, including noise obtained by a heart sound microphone or ultrasonic Doppler method, into a pulse shape and outputting the pulse;
It includes a dead period automatic setting circuit that automatically sets a dead period according to the interval between the last pulse obtained and the immediately preceding pulse, noise removing means for outputting an output pulse synchronized with the pulse as a signal pulse; and a noise removing means that automatically removes a sensitive period according to the pulse interval between the last signal pulse obtained and the signal pulse obtained immediately before it. and a fetal heartbeat cycle discrimination means that discriminates the pulse interval as a fetal heartbeat cycle when the next signal pulse is obtained during the sensitive period. Fetal heart rate measuring device.